(a) Technical Field
The present invention relates to a mold device for hot stamping, and more particularly, to a mold device for hot stamping capable of improving convenience of preheating and temperature management, by inserting a block heater having a coil structure into a lower portion of a partial softening hot stamping mold to form a heater distribution at a uniform position of a steel plate so as to keep a uniform mold temperature.
(b) Description of the Related Art
Generally, an ultra-high strength steel plate has been used to reduce the weight of a vehicle body and improve collision performance.
In this case, a technology of molding the ultra-high strength steel plate (tensile strength of 1400 MPa or more) has used a hot stamping mold.
However, in the case of a center filler outer part, the steel plate is brittle at the time of vehicle collision, and thus a fracture of the steel plate may result. Therefore, it is difficult to ensure safety of occupants of the vehicle.
To address the above problem, the related art proposes to heat a mold and then mold the mold by inserting a cartridge heater into the mold to allow a steel plate to be partially softened to a low strength (tensile strength ranging from 760 to 1100 MPa). However, the cartridge heater cannot but be inserted into a side portion of the mold, and therefore a temperature of the cartridge heater is non-uniform, such that the strength and dimension of molded panel products may be unstable.
Further, the related art includes a method of making a softening part shaped mold into an integrated type, in which a heating volume may be excessive. Therefore, it is difficult to control preheating and temperature, and deformation of the shaped mold after thermal expansion may be excessive due to the integrated type.